The present invention relates to a polishing apparatus for polishing a semiconductor wafer surface, particularly a semiconductor wafer with a device pattern formed thereon by engaging the semiconductor wafer surface with a polishing cloth to effect planarization of the wafer surface. More particularly, the present invention relates to a dressing apparatus for dressing a polishing cloth bonded to a turntable of such a polishing apparatus.
With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine, with spaces between wiring patterns also decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography and the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to have an exceptionally high degree of surface flatness or planarization. As one method for such a planarization, for example, a chemical/mechanical polishing (CMP) method has been used, in which mechanical polishing is carried out while a polishing solution having a predetermined chemical composition is supplied.
In a conventional polishing apparatus for polishing a semiconductor wafer surface, in particular, a semiconductor wafer with a device pattern formed thereon to effect planarization thereof, a nonwoven fabric is used as a polishing cloth bonded to the upper surface of a turntable.
However, the degree of integration of ICs and LSIs has been increasing in recent years. Consequently, it is demanded that a polished surface be planarized to an even higher degree. To meet such a demand, a relatively rigid polishing cloth, for example, a polishing cloth made of urethane foam has come into use.
Polishing is carried out by rotating a turntable which has a polishing cloth affixed thereto, with the polishing cloth being kept in contact with a semiconductor wafer during rotation of the turntable. During the polishing operation, however, abrasive particles (grains) and substances removed from the wafer surface during polishing tend to adhere to the polishing cloth, resulting in a deterioration of the quality of the polishing cloth, and a concomitant deleterious effect on the polishing operation. Consequently, when polishing of semiconductor wafers is repeatedly carried out using the same polishing cloth, the quality of polishing is adversely affected, and there is a danger that a wafer surface will not be evenly polished. To avoid this problem, conditioning known as "dressing" is carried out to normalize the surface of the polishing cloth before, after or during polishing of a semiconductor wafer.
When dressing a rigid polishing cloth made of a urethane foam or the like, a dresser tool comprising a material of high hardness such as diamond is generally employed. The polishing cloth is thus subject to grinding each time it is dressed. A polishing cloth made of urethane foam, for example, IC1000 (manufactured by Rodel Nitta Company) is designed to have tolerances of 1 micrometer or less each time it is dressed.
It is imperative that a polishing cloth have a flat polishing surface, in order for it to be able to polish an object uniformly to a high degree of planarity. Variations in orientation or attitude of a dresser tool resulting in non-uniformity of pressure during dressing result in a polishing cloth which does not have the requisite degree of flatness, and which is thus unable to polish a wafer to a required degree of planarity.
In the dresser tool described above, a decrease in the amount of pressure applied to a polishing cloth during dressing results in a decrease in the amount of grinding to which the polishing cloth is subject. This translates into an increase in the working life of the polishing cloth. However, such a decrease in the amount of pressure applied by a dresser to a polishing cloth during dressing has a negative influence on the stability of the dresser, whereby dressing may produce an uneven or undulating surface on a polishing cloth.